Device for filtering contaminated water with means to monitor residual contamination

ABSTRACT

A monitoring device (18, 19 or 21) for optically monitoring residual contamination of oil particles is arranged downstream of filter zone for filtering water (9) in order to block off, if necessary, a discharge line (7). Circulatory operation in which the liquid is recycled through the filter zone (9) is preferably first switched in on exceeding a threshold value for the residual contamination, in order to overcome any eventually occurring &#34;apparent contamination&#34;, for example small air bubbles, there is also provided mechanisms for distinguishing between residual and apparent contamination.

The invention relates to a device for the filtration of contaminatedliquids, in particular water which is contaminated by oil or oilcontaining substances, comprising a filter zone through which the liquidpasses and in which contaminants are to be held back, for example byadsorption, and also a monitoring device arranged at the outlet side ofthe filter zone which on inadequate action of the filter zone switchesoff a pump conveying the contaminated liquid to the inlet side of thefilter zone and/or blocks off a discharge line adjoining the outlet ofthe filter zone.

A corresponding device is described in GB-A-16 01 671. In this knownapparatus the pump is arranged at the outlet side of the filter zone andthe monitoring device reacts to the suction side pressure of the pump,i.e. to the pressure of the liquid between the outlet of the filter zoneand the pump inlet. As the throttling resistance of the filter zoneincreases with increasing contamination the suction side pressure of thepump reduces with increasing contamination. On falling below acorresponding threshold value the connection between the outlet of thefilter zone and the pump inlet is then blocked by means of a shut-offvalve.

It is known from GB-A-717 479 to supply a contamination binding agent toa contaminated liquid which can then be subsequently held back togetherwith the contamination it has bound in a filter zone through which theliquid passes. A monitoring device for the residual contamination of thecleaned liquid is arranged at the outlet side of the filter zone. Thismonitoring device reacts to the scattering of a light beam passingthrough the liquid which varies depending on the degree of the residualcontamination and controls the supply of the contamination binder, insuch a way that an excessive residual contamination is avoided.

The object of the invention is now to enable a particularly economicaloperation of filtration devices and in particular an ideal exploitationof the capacity of the filter zone.

This object is satisfied in accordance with the invention in that acirculation valve controlled by the monitoring device is provided whichcan be switched over between a throughflow position in which the outletof the filter zone is connected to the discharge line, and a circulationposition in which the outlet of the filter zone is connected to thesuction side of the pump, the pressure side of which is connected withthe inlet of the filter zone and in that in operating states in whichthe monitoring device registers an exceeding of a threshold value forthe residual contamination of the liquid emerging from the filter zonethe circulation valve can be changed over by the monitoring device tocirculatory operation and, when the circulatory operation leads alowering of the measured value for the residual contamination beneaththe threshold value, can be switched over again into the throughflowposition.

Through the possibility of switching over to circulatory operation, ifnecessary, in which the liquid to be cleaned is fed back again from theoutlet side of the filter zone to the inlet side of the latter, and thusmust pass anew through the filter zone, account is taken of the factthat different operating conditions can arise depending on the nature ofthe monitoring device in which the monitoring device registers anexcursion above the threshold value for the residual contaminationalthough in actual fact no impermissible residual contamination ispresent. Here the invention makes use of the recognition that these"apparent residual contaminants" only respectively occur for limitedtime intervals in contrast to "true residual contaminants". Accordinglythe true contaminants cannot be directly distinguished by the monitoringdevice The true contaminants are distinguished in that on exceeding thethreshold value of the residual contamination a change-over is firstmade to circulatory operation and check is made whether the degree ofthe registered residual contamination sinks beneath the threshold valuein a relative short time during circulatory operation.

For the monitoring of the residual contamination there can for examplebe provided, in accordance with an expedient embodiment of theinvention, a light emitter, the light beam of which passes through aregion of the liquid at the outlet side of the filter and also lightsensors which cooperate therewith in the manner of light barriers, withthe outlet signals of the light sensors being dependent on the lightintensities falling on the sensors and thus on the light scatteringwhich occurs in the liquid. In this arrangement the outlet signals, orthe ratio of the outlet signal levels of the light sensors, thuschange(s) in dependence on the number of light scattering particles inthe liquid at the outlet side of the filter zone. When thereforeparticles of contamination suddenly occur at the outlet side of thefilter zone, for example fine oil droplets, the light scattering in theliquid is increased with the consequence that the outlet signals of thelight sensors correspondingly change. In this manner an indication can,if necessary, be provided which reproduces the ratio between the numberof the light scattering particles present in the liquid and the quantityor mass of the liquid. A monitoring device of this kind which exploitsthe light scattering can however not reliably distinguish between thelight scattering particles of contamination and small air bubbles whichlikewise scatter the light and which can from time to time occur,because as a rule the liquid to be cleaned cannot be supplied to thefilter zone completely free of air bubbles.

If now the monitoring device first switches over to circulatoryoperation on exceeding a threshold value of the permissible number ofparticles, then air bubbles can be readily distinguished from oildroplets. The number of the air bubbles will namely be greatly reducedduring circulatory operation in the shortest time so that the number ofparticles then measured reproduces the number of oil droplets or of theparticles of contamination. When therefore after a brief recirculatoryoperation the registered number of particles sinks clearly below thethreshold value it is certain that the retaining capacity of the filterzone has not yet been used up, i.e. a change-over can bestraightforwardly be made to normal filter operation, until it is againregistered that the number of particles has exceeded the threshold valueetc.

In a further expedient monitoring device for the residual contaminationthe effect is exploited that the electrical resistance of current pathsthrough which the liquid can pass at the outlet side of the filter zonecan change in dependence on the contamination when the liquid passesthrough or over elements which are arranged within the liquid at theoutlet side of the filter zone and which are wetted or penetrated by theliquid.

In a particularly advantageous embodiment of a monitoring device whichoperates in accordance with this principle two electrodes which areconnectable to opposite poles of a voltage source are arranged on a foilweb, fabric web or fleece web which is washed by the liquid or throughwhich the liquid passes.

When clean water washes or passes through the foil web, fabric web orfleece web, for example, then the current path which leads fromelectrode to electrode has a comparatively low electrical resistance; incontrast the electrical resistance increases very rapidly oncontamination of the electrodes or of the foil web, fabric web or fleeceweb by oily contaminants, so that a rise of the electrical resistancerepresents a very sensitive signal for an undesired residualcontamination. In this case, "apparent contaminants" in the form of gasor air bubbles can however also appear which can settle out at the foilweb, fabric web or fleece web, or also at the electrodes, in particularif the filter system is temporarily stopped because no liquid to becleaned has arisen. Through temporary circulatory operation the air orgas bubbles can be removed in the shortest time so that the electricalresistance of the current path after circulatory operation forms ameasure for the actual contamination in the region of the current path.

In other respects reference should be made, with respect to preferredfeatures of the invention, to the claims and also to the subsequentdescription of advantageous embodiments of the invention with respect tothe drawing. There are shown:

FIG. 1 a schematic overall illustration of an apparatus in accordancewith the invention with the filter zone being shown in the form of alongitudinal section,

FIG. 2 a plan view of a detail of the filter zone in accordance with thesection line II--II in FIG. 1, and

FIG. 3 an illustration corresponding to FIG. 1 of a modified embodiment.

In the plant illustrated in FIG. 1 water contaminated with oil issupplied via a line 1 to the suction side of a membrane pump 2 which isconnected at the pressure side to the inlet of a filter device 3. A line4 is connected to the outlet of the filter device 3 and can be connectedvia a circulation valve 5 either--as shown in FIG. 1--with a circulationline 6 or with a discharge line 7. The circulation line 6 is connectedat the suction side of the membrane pump 2 to the inlet line 1 so thatthe water which emerges at the outlet of the filter device 3 is directedagain through the filter device 3 in the circulation position of thecirculation valve 5 when the membrane pump 2 is running.

The circulation valve 5 can be electrically actuated by a positioningmagnet which on excitation changes the circulation valve 5 over from theillustrated circulation position into its throughflow position in whichthe line 4 is connected with the discharge line 7 by which the watercoming out of the filter device 3 can be fed to the drains or can bereused. As soon as the electromagnet of the circulation valve 5 isdeenergised, the circulation valve 5 is moved back into the illustratedcirculation position by a resetting spring.

The control of the circulation valve 5 takes place in dependence on theresidual contamination of the water which flows out of the filter device3 into the line 4 in the manner which will be illustrated further below.

The filter device 3 has an upright cylindrical housing 8 with anupwardly disposed inlet and a downwardly disposed outlet. A filter set 9of cartridge-like form can be inserted from above into this housing 8after removing the upper end cover. This filter set 9 has a tubularjacket 10, the outer diameter of which is matched to the inner diameterof the housing 8. Through sealing rings 11 arranged at the externalperiphery of the jacket 10 in grooves or the like it is ensured that nowater can pass from the inlet to the outlet of the filter apparatusthrough the ring gap between the outer side of the jacket 10 and theinner side of the housing 3.

The filter set 9 is retained in the jacket 10 by net-like grids 12arranged at its end faces which are fixedly connected with the tubularjacket 10.

In the illustrated embodiment the set of filters consists of threefilter layers 13 which consist of oil absorbing filter material. In thisarrangement the filter material preferably consists of bands, cords,snippets or the like of polypropylene of greater or lesser length whichare closely packed together in the manner of a cushion. Through thisband or cord-like structure of the oil absorbing material of the filterlayers 13 one can, on the one hand, provide a desirable permeability forthe water passing through the filter device 3 and, on the other hand,labyrinth-like flow paths are provided so that oil particles carriedalong in the water can be absorbed over long paths in the filter layers13. In this way a high degree of cleaning of the water leaving thefilter device 3 can be achieved.

Plates 14 are arranged between the filter layers radial to the axis ofthe jacket 10 and a plurality of narrow bores or tubules 5 for thepassage of the water from one filter layer 13 to the next pass throughthe plates in the axial direction. The cross-section of the bores of thetubules 15 is so narrowly dimensioned that the latter act asrestrictors.

In this way, during operation of the pump 2, a certain back pressurearises above the plates 15 in the water passing through the filterdevice 3. This has the consequence that the water passing through thefilter device 3 is in each case distributed above the plates 14 over thewhole cross-section of the adjoining filter layers 13 and the adsorbentaction of the filter layers 13 can also be exploited effectively andfully close to the jacket 10.

Furthermore, the bores or tubules cause the water which passes throughto be distributed in the desired manner over the entire cross-section ofthe filter layers 13 respectively arranged beneath the plates 14. Ifnecessary the restrictor resistance relative to the vertical axis of thejacket 10 can be made smaller for the radially further outwardlydisposed bores or tubules 15 than the restrictor resistance of thefurther inwardly disposed bores or tubules 15. This can be achieved, ifnecessary, even with identical cross-section of all bores or tubules 15,for example in that the bores or tubules 15 with the lower restrictorresistance have a correspondingly shorter length. In other respects thetubules can project into the respective lower filter layer 13.

All these measures contribute to ensuring that the filter layers 13 canbe uniformly exploited, i.e. that at the end of the service life of thefilter set 9 the radially outwardly disposed regions of the filterlayers 13 have also adsorbed approximately the same quantity of oil asthe further inwardly disposed regions.

The plates 14 can thus consist in the same way as the jacket 10 of aplastic material, with a dismantlable connection between the jacket 10and the plates 14 being preferred in order to permit a regeneration orexchange of the filter layers 13 at the end of the operating period ofthe filter set 9.

In accordance with a preferred embodiment of the invention provision ismade for continuously monitoring the degree of residual contamination ofthe water at the outlet side of the filter set 9. For this purpose aby-pass line 16 which leads through a chamber 17 with a light emitter 18and also a first light sensor 19' which cooperates therewith in themanner of a light barrier can be provided at the outlet line 4. Thelight emitter 18 generates a bundled infrared light beam which passesthrough the water in the chamber 17 and is directed onto the lightsensor 19'. The light beam is differentially strongly scattered in thewater within the chamber 17 when light scattering particles, for examplefine oil droplets, are present in the water. Depending on the degree ofthe light scattering particles present in the water a differential lightintensity then falls on the light sensor 19' and at the same time afurther light sensor 19" which is disposed to the side of the axis ofthe light beam is differentially strongly illuminated. Accordingly, avarying ratio arises between the levels of the output signals of thelight sensors 19' and 19" which are dependent on the received lightintensity, depending on the number of the light scattering particles inthe water. This ratio is evaluated by a monitoring unit 23 which onexceeding a threshold value of the said level ratio, or a predeterminednumber of particles, switches over the circulation valve 5 into thecirculation position illustrated in FIG. 1. For this purpose theelectromagnet of the circulation valve 5 merely needs to be switched sothat it is deenergised.

The pump 2 initially continues in operation after switching over of theswitch-over valve 5 into the circulation position, i.e. the filterdevice 3 is operated in circulation, with the water being led anew fromthe outlet of the filter device 3 to the inlet of the same andaccordingly passing again through the filter set 9.

Through the circulation operation account can be taken of the fact thata relatively large number of light scattering particles can occur in thewater, at the outlet side of the filter set 9, without truecontamination being present. By way of example small air bubbles canoccur in great numbers since it is practically unavoidable that largerquantities of air will be carried along in the contaminated watersupplied via the line 1. Through the circulatory operation the number ofthe small air bubbles which scatter the light can be rapidly reduced sothat the "apparent contamination" of the water caused by the air bubblesis overcome at the outlet side of the filter set 9. (A venting valve 20can be arranged at the circulation line 6 for leading away largerquantities of air).

When, therefore, rapid lowering of the number of light scatteringparticles below a threshold value can be achieved through thecirculatory operation, then this means that no true contaminants arepresent and the filter set 9 is still operating adequately.

Accordingly the circulation valve 5 can again be changed over into itsthroughflow position, for example by energising the electromagnet ofthis valve.

If the threshold value of the number of light scattering particles isexceeded anew then a change-over is again first made to circulatoryoperation. Should the number of particles then not sink adequately, thenthe pump 2 is also switched off. This can, if necessary, be indicated bya special signal.

The plant must now be checked; as a rule, it will only be necessary toexchange the filter set 9.

The residual contamination of the water at the outlet side of the filterset 9 can also be monitored in other manners.

Particularly advantageous in this respect is the possibility ofdetermining the electrical resistance of a current path through whichthe water passes or which leads via elements or surfaces contacted bythe water.

In a constructionally particularly advantageous embodiment adouble-fleece layer 21 can be arranged at the lower end of the jacket 10of the filter set 9 through which the water passes and consists inprinciple of the same fiber material as the filter layers 13. Spacedapart electrodes 22 are arranged between the fleece layers--see alsoFIG. 2--and are intimately connected with the fleece layers 21 or areembedded in the latter. The fleece layers 21 thus form a carrier for theelectrodes 22.

If the electrodes 22 are connected to opposite poles of a voltage sourcethen a current path forms between the electrodes 22 and leads throughthe water or through the fleece layers, with the electrical resistanceof the current path depending very sensitively on whether or not oil hasbeen absorbed by the fleece layers 21. In this arrangement theelectrical resistance of the current path increases with increasingquantity of the adsorbed oil. As soon as a threshold value of theelectrical resistance is exceeded the discharge line 7 can beautomatically separated from the outlet line 4 in order to reliablyavoid a discharge of excessively contaminated water.

The resistance of the current path can also basically be greatlyincreased by the temporary appearance of air or gas bubbles, inparticular at the electrodes 22. For this reason provision can be madeon exceeding the threshold value of the electrical resistance to firstswitch over to circulatory operation. In this way one can first await,without the danger of introducing excessively contaminated water intothe discharge line 7, until the air or gas bubbles have been reduced bythe continued flow of the water.

Should however the electrical resistance of the current path remainabove the threshold value then the system must be checked and as a ruleit will only be necessary to exchange the filter set 9.

The fleece layers 21 with the electrodes 22 can be formed as part of thefilter set 9 at the jacket 10 so that this monitoring element is alwaysnecessarily exchanged together with the filter set 9. The electricallines for the electrodes 22 can be embedded in the material of thejacket 10 and can be connected to a cable which is led outwardly througha corresponding opening in the upper cover of the housing 8. Thus theelectrodes 22 can be connected in a particularly simple manner to anexternal monitoring unit which also supplies the electrodes 22 withcurrent.

Other methods for monitoring the residual contamination can alsobasically be used.

For example it is possible to arrange pressure sensors above and belowthe fleece layers 21 in order to determine the difference of thepressures above and below the fleece layers 21. As the restrictor actionof the fleece layers 21 increases significantly with the quantity of theoil adsorbed by these layers 21 the pressure difference is also asensitive measure for the residual contamination.

With contaminants which like oil have a lower density than water andwhich are thus urged upwardly, it is advantageous when the contaminatedwater is supplied to the filter set 9 from above or flow takes placedownwardly through the filter set 9. In this way the oil contaminationcan be kept back both by the filter material and also by the buoyancyforces.

The use of membrane pumps 2 is advantageous because in such pumps theoil contaminants--other than is the case with the customary centrifugalpiston pumps--do not form emulsions with the water from which the oil issubstantially more difficult to remove them from oil water mixtures.

FIG. 3 shows a modified layout of the filter set 9 in comparison to FIG.1.

Here the jacket 10 is formed in the manner of a cartridge with upper andlower bases 10' and 10" in which respective central openings arearranged. These central openings have, as a result of the relativelylarge thickness of the bases 10' and 10" a certain axial length whichcan optionally also be achieved by the provision of tubular stubs. Thelower central opening can also broaden somewhat conically downwardly. Incorresponding manner the upper central opening can enlarge somewhatconically upwardly. However it is basically also possible to make thesaid openings cylindrical. After removing the upper cover of the housing8 the cartridge formed by the jacket 10 can be set onto a lower stub 24which is arranged at the base of the housing 8 and which has a centralopening connected to the line 4. At the upper cover of the housing 8there is provided a further stub 25 which can be pushed into the centralopening of the upper base 10'. Seals are arranged at both stubs 24 and25 which close off the ring gap between the inner walls of openings inthe basis 10' and 10' and the outer periphery of the stubs 24 and 25. Inthis way the filter set 9 can be held unsupported within the housing 8,as illustrated in FIG. 3.

Thus, on the one hand, the seals 11 shown in FIG. 1 between the jacket10 of the filter set 9 and the housing 8 are unnecessary. Moreover, theexchange of the filter set 9 is facilitated because a spacing remainsbetween the jacket 10 and the housing 8 so that the filter set 9 iseasier to grasp.

In other respects the filter set 9 in FIG. 3 has a slightly modifiedinternal layout. Here an active carbon mat 26 is arranged beneath thelowermost adsorbing filter layer 13. Beneath this there is located asingle or double fleece layer 21 in which electrodes 22 (see FIG. 2) canoptionally be embedded in order to obtain a signal concerning theresidual contamination by measurement of the conductivity of the currentpath between the electrodes. As a rule this fleece layer 21 againconsists of the same material as the filter layers 13, i.e. for exampleof polypropylene. Beneath the fleece layer 21 there is then arranged thelower grid 12 so that all the layers of the filter set 9 through whichthe liquid to be cleaned flows are held between an upper and a lowergrid 12.

Above or beneath the grid 12 there remains within the jacket 10 acertain funnel-like free space in order to distribute the liquid runninginto the filter set or to collect the liquid running out of the filterset respectively.

The plates 14 between the filter layers can be formed in the same manneras was explained with reference to FIG. 1, i.e. bores or tubules 15 withdifferential cross-sections and/or lengths can pass through these plates14.

The jacket 10 of the filter set can consist both in the embodiment ofFIG. 1 and in the embodiment of FIG. 3 of polypropylene (in solidhomogenous form). This material is also suitable for the plates 14.

We claim:
 1. Apparatus for filtration of water which is contaminated byoil or oil containing substances and may contain air bubbles,comprising:a filter zone with an inlet and an outlet enablingcontaminated water to flow though the filter zone, the filter zonehaving an absorption capacity for retaining oil contaminants byadsorption , the filter zone thereby preventing a substantial passage ofthe oil contaminants from the inlet to the outlet until the adsorptioncapacity has been reached; an inlet line through which the contaminatedwater is provided to the inlet of the filter zone; a circulation lineconnected between the outlet and the inlet of the filter zone; adischarge line connectable to the outlet of the filter zone; acirculation valve between the outlet of the filter zone and thedischarge line and the circulation line, said circulation valve beingswitchable between a throughflow position in which the outlet of thefilter zone is connected to the discharge line, and a circulatingposition in which the outlet of the filter zone is connected to thecirculation line; a pump having a suction side and a pressure side, thesuction side being connected to the inlet line and the circulation line,the pressure side being connected to the inlet of the filter zone, saidpump feeding water from the inlet line to the inlet of the filter zonein a throughflow operation or from the outlet of the filter zone to theinlet thereof in a circulatory operation in dependence on the positionof the circulation valve; and means for monitoring the contamination ofthe water, the means for monitoring including a light emitter arrangedto pass a light beam through the water at the outlet of the filter zone,and a light sensor adapted for activation by the light beam andgenerating an output signal having a signal level dependent on lightintensities incident on the light sensor, said light intensities being ameasure of light scattering caused by light scattering particlesincluding oil particles and air bubbles in the water, the signal levelchanging as a function of both the quantity of oil particles and thequantity of air bubbles; means for determining an exceeding of athreshold value of the light scattering and a lowering of the lightscattering below the threshold value based on the output signal; means,responsive to the determining means, for changing the circulation valvefrom the throughflow position to the circulation position upon theexceeding of the threshold value of the light scattering, and forchanging the circulation valve back to the throughflow position upon thelowering of the light scattering beneath the threshold value; means formonitoring a reduction in the light scattering occurring when the valveis in the circulation position to a substantial reduction of the lightscattering indicative of air bubbles, and a negligible reduction of thelight scattering indicating that the adsorption capacity of the filterzone has been reached and substantial quantities of the oil particlesare passing the filter zone and that a renewal or regeneration of thefilter zone is necessary.
 2. Apparatus in accordance with claim 1,wherein the means for monitoring includes means for switching off thepump when the measured value of residual contamination is not loweredbeneath the threshold value within a predetermined time as a result ofthe circulation valve being switched to the circulation position. 3.Apparatus in accordance with claim 2, further comprising a displaycoupled to the means for monitoring, the display providing an indicationof the number of light scattering particles.